A. Field of the Invention
The present invention relates to a new and improved obstruction sensing edge for bifolding doors.
B. Description of the Prior Art
The current trend in mass transit door systems is to employ a fluid or pneumatically operated obstruction sensing system the leading edge of which is secured to the leading edge of an automatic door. The most popular system is the pneumatic operated sensing arrangement.
Typical arrangements employ a soft hollow extruded rubber or other elastomeric edge that is air tight except for a sensing tube extending from the hollow interior of the edge to a remotely located pressure switch. The chamber in the sensing edge is large relative to the pressure chamber in the pressure switch such that the switch is highly sensitive to changes in the shape of the leading edge. For example, if an arm were engaged by the sensing edge, the change in configuration of the chamber in the edge would send a pressure pulse through the sensing tube that is sensed in the pressure chamber in the switch. This causes the switch to actuate and recycle the system to open the door.
A significant problem in this type of obstruction sensing arrangement, particularly in bifolding doors, is that since the edges of the bifolding doors meet at the center, it is necessary that the edges engage each other to seal the door upon being closed. As the edges engage each other upon closure, a slight deformation in the chamber of the edge results in a signal to the pressure switch causing a recycling of the door. In some prior art systems this problem is overcome by detecting the location of the door and employing limit switches that parallel or cut out the recycling feature of the pressure switch. This creates the additional problem that the doors will engage an obstruction subsequent to passing the limit switch thus not recycling creating a dangerous situation.